Display screen or portion thereof with a graphical user interface



The FIGURE is a front view of a display screen or portion thereof with a graphical user interface showing our new design.

The even length broken line showing of the device illustrates environment. The remainder of the even length broken lines illustrate portions of the graphical user interface. The uneven length dash-dot lines illustrate both the display screen and the boundary of the claimed design. The broken lines form no part of the claimed design.

The stipple shading illustrates a contrast in appearance. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 